The present invention relates to an injection valve for the fuel injection in an internal combustion engine, in particular in a diesel engine, comprising a holder body in which a first passage is formed, a nozzle body of an injection nozzle which is secured at the holder body and in which a second passage is formed which is connected to the first passage and which with the latter forms a fuel infeed line for the injection nozzle, a closure mechanism for the closing off of the injection nozzle, and a sealing means for the sealing off of the connection point between the first and the second passage. Furthermore, the invention relates to a sealing means for the sealing off of the connection point between the two passages.
An injection nozzle of the initially named kind is used in internal combustion engines such as Otto engines or diesel engines in order to inject the fuel directly into the cylinder of the internal combustion engine or indirectly into an antechamber which is in connection with the cylinder. The injection valve should introduce an amount of fuel which is as precisely metered as possible at a predetermined time point into the cylinder or the antechamber respectively as a finely distributed mist. For this purpose the injection nozzle of the injection valve is closed off by a closure mechanism, for example a nozzle needle, which is mechanically prestressed and which opens the injection nozzle briefly for the fuel injection, with the emerging fuel being atomized by the injection nozzle. In order that a sufficient amount of fuel is injected and the fuel is atomized as finely as possible in spite of the short injection duration, the fuel is fed in to the injection valve with a pressure of 1400 bar and more in the known injection systems, such as for example the common rail injection system.
In order that the closure mechanism which is required for the closing off of the injection nozzle can be installed, the known injection valves are constructed of several parts. Thus the actual injection nozzle is secured together with the closure mechanism at a holder body. The fuel infeed takes place via a first passage which is formed in the holder body and which is connected to a second passage which is formed in the nozzle body of the injection nozzle. The second passage ends in a pressure chamber or in an outlet opening of the injection nozzle. In order to avoid a leakage of the fuel between the holder body and the nozzle body, the connection point between the two passages is sealed off by a sealing means, such as for example a sealing disc, or through correspondingly machined contact surfaces between the holder body and the nozzle body.
Since the fuel which is located in the fuel supply line is under very high pressure, as explained above, the sealing means at the connection point between the passages must be designed in such a manner that it can withstand very high stresses. For this reason in the known injection valves the sealing surfaces which are formed at the holder body and the nozzle body, at which the sealing means lies in contact, and the sealing means itself must be manufactured with very high manufacturing precision and high surface quality. Moreover, the sealing means which is arranged between the holder body and the nozzle body must be pressed together with such a high bias force that the connection point between the two passages does not leak in spite of the high pressures.
The object of the invention is to further develop an injection nozzle or, respectively, a sealing means of the initially named kind in such a manner that the connection point between the passages is sealed off in a simple manner and can also withstand high pressures.
This object is satisfied in the injection nozzle of the initially named kind in that a sleeve which protrudes at least into the first passage of the holder body or into the second passage of the nozzle body serves as a sealing means.
In the injection valve in accordance with the invention the sleeve, which protrudes into the passage, is pressed by the high pressure acting in the interior of the fuel infeed line against the inner wall of the passage and conforms to the surface of the latter, through which a leakage-free sealing off at the connection point between the passages is achieved. Moreover, lower demands need be placed on the manufacturing precision and the surface quality both during the manufacture of the passage and in the manufacture of the sleeve than in conventional injection valves since the sleeve, which conforms to the inner wall of the passage through the high pressure, compensates possible unevennesses or measurement deviations. Furthermore, the assembly of the injection valve is facilitated since the sleeve serves at the same time as a centering aid which simplifies the exact mutual orientation of the holder body and the nozzle body and the mutual alignment of the passages.
Advantageous further developments result from the description, from the drawings and from the respective subordinate claims.
Thus it is particularly advantageous when the sleeve has a section of smaller outer diameter. Through this design of the sleeve it is achieved that the sleeve is more strongly widened by the high pressure in the weakened section of smaller diameter than in the non-weakened sections of the sleeve and the sleeve conforms even better to the inner wall of the passage, with it bulging slightly outwardly in a convex manner at the same time. Through the convex deformation the transition between the section of smaller diameter and the adjacent, non-weakened section of the sleeve lays itself linear at the inner wall of the passage, through which a particularly good sealing action is achieved. In this the section of smaller diameter is preferably arranged in the region of the connection point between the passages in order to achieve as great a sealing action at the connection point as possible.
In a preferred embodiment of the injection valve the sleeve is formed as a separate component which is inserted into the fuel infeed line during the assembly of the injection valve and protrudes both into the first passage of the holder body and into the second passage of the nozzle body. This has the advantage that through the intentional selection of sleeves which differ in the design of the inner periphery the flow conditions of the fuel which flows through the fuel infeed line can be intentionally influenced.
In order that the sleeve has a secure hold in the fuel infeed line it can be pressed in into the passages so that a press fit is formed between the sleeve and the inner wall of the respective passage.
Alternatively, the sleeve can be formed integrally with the holder body or with the nozzle body. The sleeve then serves as a tubular prolongation of the first or of the second passage, respectively, which protrudes into the second passage of the nozzle body or the first passage of the holder body respectively after the assembly of the injection valve. In this embodiment of the injection nozzle there is the advantage that in the assembly of the injection valve there are only few components to be assembled.
Furthermore, it is advantageous when at least one of the passages has at its end which faces the other passage a section with a larger inner diameter in which the sleeve is accommodated or pressed in, respectively. If the sleeve is designed as a separate component, as in the first of the two exemplary embodiments described above, the sleeve can rest on the offset which is formed in the passage, whereby on the one hand a moving about of the sleeve in the fuel infeed line is effectively prevented and, on the other hand, the sleeve is held by the offset in a predetermined position in the fuel infeed line.
The fuel infeed line can be designed as a simple passage which extends through the holder body and the nozzle body. On the other hand the passages which form the fuel infeed line can also be used as a reception for the closure mechanism of the injection nozzle. Thus the passages serve in a preferred embodiment of the injection nozzle not only as a fuel infeed line but also at the same time as a needle guide for a nozzle needle which acts as a closure mechanism by means of which the injection nozzle can be closed off. The nozzle needle is movable in the longitudinal direction of the needle guide between a rest position in which it closes off at least one injection hole in the nozzle body which is connected to the second passage and an opening position in which it at least partly opens the injection hole. The fuel is forwarded in this embodiment along the nozzle needle through the passages which serve as the needle guide and is ejected out of the injection hole which is formed at the end of the second passage. Through the connection of the two passages which serve as the needle guide to the sleeve it is also achieved that the longitudinal axes of the passages extend in a definite manner relative to one another and the nozzle needle bends at most slightly transversely to its longitudinal direction during its movements in the needle guide.
In order to influence the flow behavior of the fuel which flows through the fuel infeed line which serves as a needle guide, it is furthermore possible to use a nozzle needle which has a cross-sectional shape which varies in its dimensions over its length. Thus the nozzle needle preferably has at least one section of larger diameter which reduces the cross-sectional area through which the fuel flows, which is bounded by the inner wall of the fuel infeed line and the jacket surface of the nozzle needle, and which acts as a restrictor which increases the flow resistance.
The section of larger diameter is preferably formed at the nozzle needle with a spacing from the needle tip so that the cross-sectional area of the fuel infeed line through which the fuel flows is larger between the needle tip and the section of larger diameter of the nozzle needle than the cross-sectional area of the fuel infeed line which is flowed through in the region of the section of larger diameter of the nozzle needle. Through this it is achieved that the fuel has a lower flow velocity in the longitudinal section of the fuel infeed line in which the needle tip is located than in the longitudinal section of the fuel infeed line in which the section of the nozzle needle of larger diameter is located. This has the result that the amount of fuel which is located near the needle tip when the injection valve is opened flows off more rapidly as a result of the lower flow resistance caused by the lower flow velocity in this longitudinal section than the fuel which flows after it through the longitudinal section of the fuel infeed line which is narrowed by the section of larger diameter of the nozzle needle, which fuel admittedly has a higher flow velocity, but however must also overcome a greater flow resistance. Through this a pressure difference arises between the two longitudinal sections of the fuel infeed line, with the pressure being greater in the longitudinal section of the fuel infeed line in which the section of the nozzle needle of larger diameter is located. The higher pressure assists in turn the closure movement of the nozzle needle into its rest position. In order to amplify this effect it is furthermore proposed to form at the nozzle needle between the needle tip and the section of larger diameter a section, the diameter of which is smaller than the average diameter of the nozzle needle.
In the same way the flow behavior of the fuel in the fuel infeed line can also be influenced through the cooperation of the sleeve with the jacket surface of the nozzle needle so that the sleeve forms a restrictor point with the nozzle needle when the nozzle needle is moved into its opening position.
In a preferred further development of the above described injection valve with nozzle needle, the nozzle needle is prestressed into its rest position by at least one spring element which is provided in the first passage of the holder body, with the spring element effecting or assisting respectively the closure movement of the nozzle needle.
Furthermore, it is advantageous if the inner periphery of the sleeve, which is deformed by the high pressure, together with the outer periphery of the nozzle needle forms a space which extends in ring shape transversely to the longitudinal direction of the nozzle needle and through which the fuel flows through. Through a corresponding design of the cross-sectional shape of the ring-shaped space in the longitudinal direction of the nozzle needle the flow behavior of the fuel can be intentionally influenced. Thus it is possible to use a sleeve which has an inner periphery which varies in its dimensions over its length and which together with the preferably cylindrical outer periphery of the nozzle needle forms a restrictor point.
Since a definite position between the holder body and the nozzle body is already predetermined by the sleeve, only a further rotational securing, for example in the form of a centering pin, is now required by means of which the position of the nozzle body relative to the holder body is fixed.
In an alternative embodiment a feather key is preferably used as a rotational securing. For this purpose a groove into which the rotational securing can be laid in is formed in each case at the holder body and at the nozzle body. As soon as the holder body is mounted at the nozzle body the two grooves are aligned with respect to one another in such a manner through a rotation of the holder body relative to the nozzle body that the two grooves, which are open at the mutually facing ends, align with one another. Then the rotational securing is inserted into the grooves.
The sleeve serves in this embodiment additionally as a centering aid, which on the one hand facilitates the mutual alignment of the grooves, and on the other hand together with the rotational securing prescribes a definite position of the nozzle body relative to the holder body in order that the injection holes which are formed at the nozzle body take on their predetermined angular positions. At the same time it is achieved through the cooperation of the sleeve with the rotational securing, which is accommodated in the grooves, that the end sides of the holder body and of the nozzle body which mutually lie in contact lie more uniformly in contact than in known rotational securings for injection valves, whereby the sealing action between the end sides is further increased.
It is particularly advantageous when the grooves are formed in each case at the jacket surfaces of the holder body and the nozzle body and extend in the axial direction of the injection valve, whereas at the same time a nozzle tightening nut which secures the nozzle body at the holder body secures the rotational securing which is accommodated in the grooves against a dropping out. On the one hand such grooves can be produced without a great effort, and on the other hand through the axial course of the grooves at the jacket surfaces both the nozzle body and the holder body can be reduced in their dimensions transversely to the longitudinal direction of the injection nozzle with the strength remaining the same. If the dimensions of the nozzle body and the holder body are retained unchanged, on the other hand, the strength of the injection valve is increased.